1. Field of the Invention
The present invention relates to a method of defining regions of a group III-V compound and particularly to the use of a carbon coating as a mask for defining the regions of the material.
2. Description of the Prior Art
In making various types of devices of single crystalline or polycrystalline material, such as various types of semiconductor devices, optical or acoustical wave guides etc., it is often desirable to form defined regions of the crystalline material, e.g. to form spaced regions of the material on a substrate or to form regions of a particular shape and size on a substrate or to provide recesses or cavities in a body or layer of the material. One technique which has been used to form spaced or particularly shaped regions of a crystalline material on a substrate is to first form a layer of the crystalline material on the substrate, such as by epitaxial or pyrelytical deposition. A layer of a resist material is then provided on the surface of the portions of the crystalline material layer which are to be retained. The remaining portions of the crystalline material layer which are not covered by the resist are then removed, such as by etching. This technique has a problem in that in etching away the uncovered portions of the crystalline material layer it is difficult to control the depth of the etching to insure that all of the undesired crystalline material is removed but the substrate material is not removed. Also, the etching often undercuts the resist material so as to change the shape and size of the area of the crystalline material which is to remain. In addition, in this technique, the resist material is applied to the area of the crystalline material which is to remain and unless the resist material is completely removed it can contaminate the crystalline material.
Another technique which has been used to form spaced or particularly shaped regions of crystalline materials on a substrate is to apply a masking material on the surface of the substrate except where the crystalline material is to be provided. The single crystalline material is then deposited on the surface of the substrate not coated with the masking material and is not deposited on the masking material. The masking material is then removed leaving the defined regions of the crystalline material on the substrate. To carry out this technique the masking material must be of a material which will not nucleate the growth of the crystalline material so that the crystalline material will not deposit on the masking material. Also, the masking material must be capable of being removed without adversely affecting the deposited crystalline material. Silicon dioxide is the material which has heretofore generally been used as the masking material. Although silicon dioxide does not serve as a good nucleation site for the growth of the crystalline material, some of the material will deposit on the silicon dioxide. However, silicon dioxide is relatively porous so that in order to prevent the crystalline material from depositing on the substrate through the pores in the silicon dioxide a relatively thick coating of the silicon dioxide must be used. This makes the silicon dioxide masking layer harder to remove without adversely affecting the deposited single crystalline material.